The present invention relates to turbojet engines, more particularly a system for attaching a rotor blade to a rotor disk for such engines.
It is well known in the art to attach rotor blades to a turbine rotor disk of a turbojet engine by axially inserting a foot portion of the rotor blade into a notch defined in the periphery of the rotor disk. However, this system of assembly typically causes two problems: first, it has been virtually impossible to axially lock each rotor blade in the rotor disk in a manner which not only allows a single blade or the entire blade set to be disassembled and, at the same time reliably retains the blades in their locked positions; second, sealing between the upstream and downstream zones on either side of the rotor disk has been difficult to achieve effectively, thereby lowering the efficiency of the turbojet engine. The spaces between the notches formed in the rotor disk and the foot portions of the rotor blades can, if not properly sealed, allow substantial quantities of air to move beneath the blade feet from a downstream position and recirculate toward the upstream of the compressor thereby lowering the compression ratio of the compressor and resulting in a decrease in the overall efficiency of the tubojet engine.
It is known to axially position the rotor blades relative to the rotor disk by the engagement of a flange formed on the rotor blade with the upstream surface of the rotor disk and to lock the blade into position by an elastically deformable split ring. Typically, the split ring is radially compressed during assembly so that it can be inserted into an opening in the rotor disk. The split ring then expands inside an annular groove formed in the rotor disk and in the blade feet.
In another system, illustrated in French Pat. No. 2,501,283, a ring is notched so as to simultaneously enter a circular slot formed in the rotor disk and in slots formed in the blade flanges. The ring is then rotated slightly such that a solid portion of the ring engages the slots formed in the blade flanges and the slot in the rotor disk. While such a system is effective at locking the rotor blades, it suffers from the drawback of poorly sealing the air at the interface of the blade feet and the rotor disk notch.
The system shown in British Pat. No. 1,512,882 attempts to solve this problem by using ring-sealed plates cooperating with a circular groove in the rotor disk and with grooves on the blade platforms. An O-ring in the rotor disk groove cooperates with a frusto-conical surface on the plates to compress them by centrifugal action against the platform grooves. Such an arrangement improves the sealing in the area of the blade feet, but presents difficulties in relation to small-diameter compressor rotor disks. Furthermore, this system requires a large number of parts, thereby increasing the complexity of the installation and maintenance.